Conductive footwear



June 23, 1942. L. J. MONAHAN 2,287,744

GONDUCTIVE FOOTWEAR Filed Oct. 8, 1941 Patented 'June 23, 1942,

UNITED S ATES INPVATENT oFFics I oonnuczi v ri orwnaa Leo J. Monahan, Humboldt, Tenn., minor to O'Donnell Shoe Company, Humboldt, Tenn, a

corporation of Minnesota Application October a, air-serial No. 414,172 I 3 Claims. (Cl. 175-264) The present invention relates to conductive footwear and more particularly to a conductive overshoe or outer sandal designed to be worn over an ordinary non-conductive shoe or other article of footwear for the purpose of establishing a conductive path to ground for static electrical charges that may be gathered in the human It has recently been the custom in manyindustrial plants, as a precautionary measure,

to furnish the workmen and other employees in the plant with a specially designed conductive shoe which is so designed that static electrical charges are not readily gathered in the human .body and that such charges, if gathered, are

passed to ground through the outer sole of the shoe.

Conductive shoes of the present character are found useful in many so-called hazardous occu-' pations as for example, in powder and munitions plants, in gasoline refineries, gasoline warehouses, and imilar establishments where the atmosphere is apt to be laden with explosive gases or explosive dust. Indeed, in many instances at such establishments, it is a requirement that even visitors, inspectors and other persons tem-.

' which are apt to be present in ordinary street shoes. Such metallic articles constitute a fire hazard in that they are liable to generate frictional or thermal discharges (i. e. sparks) when subjected to abrasion. A

Thus, in establishments. where explosive gases, vapors or dust is present, there is a dual explosive hazard arising (1) from possible accldental discharge of static (electronic) electricity from the human body and consequent generation of an igniting spark, and (2) a similar hazard arising from creation of a frictional (thermal) spark due to abrasion between twosurfaces one of which is usually of metal.

The principal object of the present invention is to provide a conductive outer shoe, overshoe or sandal, especially designed foruse by visitors and other persons temporarily admitted to indusveniently worn over the ordinary non-conductive street shoe, and which is provided with means whereby the body of the wearer is effectively grounded at all times. In other words, the. im-

proved conductive overshoe or sandal comprising the present invention, in effect, provides an electrical shunt around the ordinary non-conductive shoe whereby static electrical charges gathered in the human body are passed around the latter shoe and are oonductedto ground.

It is another object of the present invention to provide such an outer shoe, sandal or the like wherein the fastening means employed for maintaining the shoe in position also serves as. an electrical conductor to lead static charges from the body.

Yet another object of the invention is to .provide a conductive overshoe of the character set forth above which is characterized by an absence of metal inserts, fastening's and the like which ordinarily would constitute an explosion hazard due to possible generation of frictional or thermal sparks.

Another and important object of the invention is to provide a conductive overshoe which, unlike shoes which depend for their grounding ac-- tion upon metallic conductors, presents a relatively high resistance to electrical currents, thus passing these currents'slowly to ground without the creation of a statically generated spark. A shoe of this character, in addition to affording protection against the generation of static discharges, will also effectively prevent generation of sparks from frictional causes and it has been found that no amount-of frictional abrasion performed on the shoe will result in the generation of a spark.

It is still another object of the invention to provide a conductive overshoe or the like which may conveniently be made in various sizes and which, with a minimum of effort may be slipped onto an ordinary shoe and fastened thereon securely, and which at the same time, may just as readily b..- removed therefrom.

The provision of a conductive overshoe. or

sandal which is extremely rugged and durable and which therefore is possessed of a relatively long life, one which is comfortable to the foot of p the user, are further desirable features that have been home in mind in the production and development of the present invention.

Other objects and advantages of the present invention will become readily apparent as the trial plants, and the like, which may be conwing description ensues.

In the accompanying single sheet of drawings forming a part of this specification:

Fig. 1 is a perspective view of one. form of conductive sandal manufactured in accordance with the principles of the present invention, i

Fig. 2 is a longitudinal sectional view taken through a modified form of conductive overshoe, and

Fig. 3 is a sectional view similar to Fig. 2 showing a further modified form of sandal.

Referring now to the drawing in detail and specifically to Fig. 1, wherein one form of the improved conductive sandal is shown, the sandal includes a relatively thick one-piece sole l having a ball portion l2 and a heel portion l4 connected by an arch portion IS. A web or strap I8 extends across the ball portion I2 of the sole l0 and is anchored at its ends to the sole in any suitable manner, as for example, by stitching 20. The sole I0 is formed of conductive rubber or of leather which has been treated to render the same conductive. clusion of a quantity of carbon particles in the rubber batch serves to impart to the finished product the desired conductivitywhile in the case vof leather, impregnation with a suitable conductive halogen salt solution renders the leather permanently conductive.

The strap It may be formed of either conductive material or of non-conductive material, its inherent construction not being critical. As shown, this strap includes non-resilient pieces of conductive rubberized fabric 22, connected together by an elastic strip 24. The elastic strip 24 provides an automatically adjustable strap undershoe shown in dotted lines at 26 may be I accommodated. The strap I6 is adapted to extend over the vamp or toe portion of the ordinary non-conductive overshoe and, since this strap makes no contact with the skin of the wearer, it is immaterial whether any or all portions thereof are conductive or non-conductive. For convenience, however, in the manufacture of the shoe, the side pieces 22 are formed of conductive rubberized fabric to harmonize with other conductive. portions of the shoe as will appear presently.

. Secured in any suitable manner, as for example, by stitching 28 or the like, to the heel portion l4 of the sole i0 is an ankle piece 30 having fastening ears 32 at opposite sides thereof'adjacent the top. Relatively small holes 34 are formed in the cars 32 and a fastening strip 36 which is of a width somewhat greater than the diameter of the holes 34 passes through the latter. The strip 36 is adapted to be wound one or more times around the ankle of the user and then had as indicated at 38.

The material of the ankle piece 30' is essentially conductive. In the present instance, this piece is formed of a rubberized fabric in which the rubber is of a composition that is conductive. This rubber component material is comprised of a rubber compound containing carborr particles while the to the entire structure. If desired, the ankle 'piece'30 may be formed of fabric or leather which has been treated in any suitable manner, as for example, by impregnation with a conductive salt solution, to render the same conductive.

The fastening strip 36 is likewise formed of a conductive material, preferably the same material as the ankle piece 30. This strip, being slightly wider than the diameter of the'holes 34,

is atall times in electrical contact with the ankle piece 30 which in turn, is in electrical contact with the sole l0.

In the use. of the improved sandal, the wearer may roll his sock or stocking downwardly, and over the upper margin of the ankle piece" if desired. This will permit the fastening strip 36 to be brought-into direct contact with the skin of the wearer. It is not absolutely necessary, however, for the wearer to adjust his sock or stocking inasmuch as most articles of this character are quite thin and porous and ample electrical contact may be had with the skin through the sock.

The extent of conductivity of the material of .the sandal may be varied throughout a wide In the case of'rubber, the-inrange of resistivity. The shoe as at present man ufactured, is such that a pair of test wires having alligator clips fastened to the extreme tip of the toe portion of the shoe and to the fastening strip 36 gives a reading on an ohmeter of about 500,000 ohms. A resistance as high as 2 megohms will conduct static charges quite slowly to ground, while a resistance of about 50,000

ohms is ordinarily ample to prevent creation of a spark upon discharge of static charges. Any

resistance lower than this is liable topermit creation of a spark upon discharge'of static charges.

7 The principle of operation of the conductive overshoe shown in Fig. 2 is substantially the same as that described above. In this form of the invention, a one-piece molded rubber overshoe 60 whereby undershoes of varying sizes such as the ing in combination, a bottom sole formed of rel-' fabric serves to lend coherence of the type commonlyreferred to as a halfrubber," is formed of conductive material and is providedwith a conducting tab 52 at the extreme top of the heel portion 54. This tab in addition to serving as a pull-on device, is adapted to be inserted into the rear portion of an ordinary non-conductive undershoe-and provide electrical contact with the Skin of the wearer through the sock or stocking. Static charges are thus conducted from the tab to the remaining portions of the-overshoe and from thence to ground.

In Fig. 3,,a modified form of conductive sandal .is shown. This form of the invention is similar to thatshown in Fig. 1, the main points ordeparture being in the provision of a heel well as .at 60 to prevent shifting of the sandal on the under shoe.- In addition, the ankle piece 62 is formed of non-conductive material and a conductlve connector 64 is provided at'the rear of ,the shoe and extends upwardly above. the shoe and is adapted to establish contact with the skin through the heel portion of the sock and to electrically connect the foot of the wearer with" the sole 66 of the shoe. An ordinary snap fastener 10 is utilized to fasten the ears 60 in overlapping relationship as shown.

What is claimed is: Y I l. Aconductiveovershoe adapted to be worn over anordinary non-conductive shoe comprisatively soft resilient material which offers a relatively high resistance to passage of electrical charges, said sole having a toe portion and a heel portion, a heel piece secured to the heel portion and extending upwardly therefrom, said heel piece being also formed of such conducting material and making electrical contact with the sole portion, and a flexible fastening strap electrically connected to the heel piece and adapted to be tied around the ankle of the user. above the noneconductive shoe, said vstrapn' being also formed of such conducting material whereby static electrical charges gathered in the human body are shunted around the non-conductive shoe by being passed through the strap, heel piece and bottom sole.

2. A conductive overshoe adapted to be worn over an ordinary non-conductive shoe comprising in combination a bottom sole formed of relatively soft resilient material which offers a relatively high resistance to passage of electrical charges, said sole having a toe portion and a heel portion, a heel casing in electrical contact. with and extending upwardly from the heel portion and likewise formed of such conducting material, and means carried b the heel casing in electrical contact therewith for electrically connecting the latter to the ankle of the user.

3. A one-piece molded overshoe formed in its entirety of conductive material offering a relatively high resistance to passage of electrical charges, said overshoe being adapted to be worn over anordinary non-conductive shoe, said overshoe including a bottom sole, and a shoe upper portion including a heel casing, and a flexible tab also formed of conductive material extending outwardly from the upper edge of the heel casing and adapted to be received between the ankle of LEO J. MONAHAN' 

